8-cyano-5,6,7,8-tetrahydroquinoline derivatives

ABSTRACT

The invention relates to novel 8-cyano-5,6,7,8-tetrahydroquinoline derivatives which are intermediates for the preparation of corresponding 8-thioamides. Some of the 8-cyano compounds are anti-ulcer agents.

The invention relates to novel 8-cyano-5,6,7,8-tetrahydroquinoline derivatives and to pharmaceutical compositions containing the novel derivatives and is a continuation-in-part of our co-pending application Ser. No. 600,257 filed July 30, 1975 which is a continuation-in-part of our Ser. No. 460,265 filed Apr. 11, 1974 both now abandoned, which in turn is a continuation-in-part of our Ser. No. 403,289 filed Oct. 3rd, 1973, and now abandoned.

The invention provides a compound of formula I ##STR1## and acid addition salts thereof with pharmaceutically acceptable acids, wherein R¹, R² and R⁶ are the same or different and are selected from hydrogen, trifluoromethyl, alkyl of 1 to 6 carbon atoms, phenylalkyl wherein the alkyl group has 1 to 6 carbon atoms, or phenyl groups, or R¹ and R² taken together represent an alkylene chain --CH₂ (CH₂)_(n) CH₂ ⁻ wherein n is an integer from 1 to 3, R⁷ represents hydrogen or from 1 to 3 groups selected from alkyl groups of 1 to 6 carbon atoms, which may be substituted by alkoxy of 1 to 6 carbon atoms or trifluoromethyl; phenylalkyl wherein the alkyl group has 1 to 6 carbon atoms and phenyl groups, and when R¹ and R² taken together form an alkylene chain the resulting ring may be substituted by from 1 to 3 R⁷ groups as above defined, X is cyano and any of the phenyl groups or the phenyl portion of any phenylalkyl groups R¹, R², R⁶ and R⁷ may be substituted by alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 carbon atoms, halogen, nitro or trifluoromethyl, with the provisos that (1) when R¹ and R² or R² and R⁶ are both alkyl they are selected from normal and secondary alkyl groups and (2) when two alkyl groups R⁷ are present on the same carbon atom then they are both n-alkyl groups and when two R⁷ alkyl groups are present on adjacent carbon atoms they are selected from normal and secondary alkyl groups.

R⁷ may be in the same position as X.

When any of R¹, R², R⁶ or R⁷ is an alkyl radical this is a lower alkyl radical which may have a straight or branched chain, having from 1 to 6 carbon atoms, e.g. methyl, ethyl, n-, and iso-propyl and n-, s- and t-butyl, R⁷ may be a gem-dimethyl group and when a single radical may be on the same carbon atom as the group X. The term alkyl radical is also intended to embrace cyclic alkyl radicals e.g. cyclobutyl, cyclopentyl and cyclohexyl. When any of R¹, R², R⁶ or R⁷ is a phenyl alkyl radical the alkyl portion may be as discussed above for an alkyl radical.

Particularly preferred compounds are those in which one of R¹, R², R⁶ and R⁷ is methyl and the others are hydrogen.

Thus the present invention provides, in one preferred aspect, compounds of formula II ##STR2## and acid addition salts thereof, wherein one of R¹, R², R⁶ and R⁷ are selected from hydrogen and methyl.

The compounds of formula I can form acid addition salts with inorganic acids e.g. hydrochloric, hydrobromic, sulphuric or nitric acids, or organic acids e.g. fumaric, maleic or tartaric acids. These acid addition salts are included in the invention.

In the compounds of formula I the carbon atom to which X is attached is asymmetric. Consequently the compounds can exist in optically active d and l forms. These optically active forms and the racemates are included in the invention. The optically active forms may be separated by standard techniques either by formation of an acid salt with an optically active acid or by use of an optically active base with a precursor compound in which X is COOH and conversion of the desired isomer to a nitrile of formula I.

Compounds of formula I are intermediates for compounds of formula I wherein X is CSNHR³ and R³ is hydrogen or lower alkyl. These thioamides are anti-ulcer agents which have anti-ulcer activity as determined by the method of Brodie and Hanson, J. Applied Physiology, 15, 291, 1960 or anti-secretory activity as determined by the test mentioned below. In the above test 5,6,7,8-tetrahydroquinoline-8-thiocarboxamide, 2-phenyl-, 2-t-butyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide and 2-, 3 and 4-methyl-, 3,4-dimethyl-,3,5-dimethyl- and 3,6-dimethyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide have shown good activity. Compounds of formula I, wherein X is CSNHR³ often display anti-secretory activity in the test of H. Shay, D. Sun and H. Greenstein, Gastroenterology 1954, 26, 906-13. For instance 5,6,7,8-tetrahydroquinoline-8-thiocarboxamide, the 2, 3 and 4-methyl and 3,6-dimethyl analogues thereof exhibited good activity in this test.

Nitriles of formula I wherein X is CN are usually active in one of the above tests and such nitriles are anti-ulcer agents. Compounds which exhibit activity in the above anti-ulcer or anti-secretory tests are regarded as anti-ulcer agents.

The compounds of formula I may be prepared by various methods, all of which are included in the invention.

A general method of preparing the compounds of formula I comprises treating a corresponding compound in which X is hydrogen by known methods to introduce the nitrile group X.

The nitriles of formula I may be prepared from the corresponding amides of formula I wherein X is CONH₂ which in turn may be prepared from esters of formula I, wherein X is CO₂ R⁵ and R⁵ is lower alkyl.

A method for preparing compounds of formula I in which X is CO₂ R⁵ comprises carboxylating a corresponding compound wherein X is hydrogen, to obtain a compound of formula I in which X is COOH or a metal salt thereof, and if desired esterifying the product with an hydroxyl compound R⁵ OH, wherein R⁵ is lower alkyl. The carboxylation may be achieved by preparation of a metal salt of compound of formula I wherein X is COOH, by treating a corresponding compound in which X is hydrogen, with a metal alkyl, followed by treatment of the product in situ with carbon dioxide, conveniently by bubbling CO₂ gas into the reaction mixture. The compound of formula I in which X is CO₂ H is obtained by treatment of the product, a metal salt of a compound of formula I in which X is COOH, with acid e.g. hydrochloric or hydrobromic acid. A convenient method is to treat a solution of the salt with gaseous hydrogen chloride. The metal alkyl may be one of a monovalent metal e.g. MR¹⁰ wherein M is sodium, potassium or lithium and R¹⁰ is alkyl, aryl or aralkyl or one of a divalent metal M(R¹⁰)₂ wherein M is calcium or magnesium. A convenient reagent MR¹⁰ is lithium phenyl or n-butyl lithium.

It has been found that when a compound of formula I in which R¹ is methyl and R², R⁶ and R⁷ are hydrogen and X is hydrogen is carboxylated, the carboxylation may occur either on the methyl group R¹ or at the desired X position. Usually a mixture of desired and undesired product is formed but the desired product can be separated during subsequent work-up.

The esterification of a compound of formula I in which X is CO₂ H may be carried out using an hydroxyl compound R⁵ OH, wherein R⁵ is as defined above except hydrogen according to standard procedures, e.g. in the presence of an acid catalyst e.g. some concentrated sulphuric acid or after saturation with hydrogen chloride gas or a Lewis acid e.g. boron trifluoride if desired with heat or treatment of the silver salt, (X is COOAg) with an iodide R⁵ I wherein R⁵ is as defined above, except hydrogen.

The yield of ester can be improved by introducing a further quantity of the metal alkyl after the CO₂ treatment, followed by a further amount of CO₂. It is believed that the further quantity of metal alkyl and CO₂ gives the bis acid metal salt of formula IV ##STR3## wherein R¹, R², R⁶ and R⁷ are as defined in connection with formula I and M is the metal of the metal alkyl e.g. sodium, potassium or lithium, and this salt spontaneously decarboxylates during the esterfication.

A further method for preparing esters of formula I wherein X is CO₂ R⁵ comprises treating a compound of formula I as defined above wherein X is a hydrogen atom with a metal alkyl (as defined above) and then treating the product with a haloformate of formula HalCOOR⁵ wherein Hal is a halogen atom e.g. chlorine or bromine and R⁵ is as defined above. The product is usually a mixture of the desired compound of formula I wherein X is CO₂ R⁵ and the corresponding bis-ester of formula V ##STR4## These bis-ester are useful for preparing the corresponding compounds of formula I wherein X is CO₂ H. We have found that this mixture of mono and bis esters can be converted directly to the corresponding compound of formula I where X is CO₂ H, by saponification with an alkali or alkaline earth metal hydroxide to give a mixture of the metal salt of the mono acid of formula I wherein X is CO₂ H and the metal salt of the diacid of formula V wherein R⁵ is H. Treatment of this mixture with a mineral acid e.g. hydrochloric acid gives the desired acid of formula I wherein X is CO₂ H since the diacid spontaneously decarboxylates to form the mono acid.

The product of the haloformate reaction may be treated with a further quantity of the metal alkyl followed by a further quantity of the haloformate thereby producing more of the bis ester (V).

A further method for preparing compounds of formula I in which X is CO₂ H comprises decarboxylation of a compound of formula V ##STR5## wherein R¹, R², R⁵ and m are as previously defined. The decarboxylation can be carried out by heating the dicarboxylic acid of formula V wherein R⁵ is hydrogen. Usually the dicarboxylic acid is prepared in situ by hydrolysis of the corresponding di-ester, wherein R⁵ is as defined above except hydrogen. The hydrolysis and decarboxylation may be carried out by heating with a dilute mineral acid e.g. HCl or sulphuric acid or the diester may be saponified with alkali e.g. sodium or potassium hydroxide. The resulting salt is then acidified and decarboxylated by heating.

Compounds of formula I, in which X is CONH₂ may be prepared by treatment of a corresponding compound of formula I wherein X is COCl or CO₂ R⁵ and R⁵ is lower alkyl with ammonia to give a compound of formula I in which X is CONH₂. Conveniently a compound of formula I wherein X is CO₂ R⁵ wherein R⁵ is lower alkyl, especially methyl or ethyl, is treated with ammonia.

The acid chlorides may be prepared by treatment of the corresponding acid of formula I, wherein X is CO₂ H with thionyl chloride, phosphorus oxychloride or phosphorus pentachloride.

The acid chlorides may be prepared by treatment of the corresponding acid of formula I, wherein X is CO₂ H with thionyl chloride, phosphorus oxychloride or phosphorus pentachloride.

A further process for preparing compounds of formula I as defined above wherein R¹ and R² are as defined above and X is CONH₂, comprises treating an ester compound of formula I, wherein X is CO₂ R⁵ and R⁵ is lower alkyl with an amide of formula R⁹ CONH₂ or a salt thereof wherein R⁹ is hydrogen or lower alkyl in the presence of an alkali-metal alkoxide.

Preferably a molar equivalent of alkali-metal alkoxide is used for each mole of ester of formula I. The alkali-metal alkoxide may be one derived from a lower alkanol having 1 to 6 carbon atoms e.g. methanol or ethanol. The alkali-metal is preferably sodium.

The amide R⁹ CONH₂ is preferably one in which R⁹ is hydrogen or methyl. Thus preferred amides are formamide and acetamide. Salts, especially alkali-metal salts of these amides may be used as starting materials.

The reaction may be carried out by heating the reactants together.

The amides of formula I, wherein X is CONH₂ may also be prepared by partial hydrolysis of the corresponding nitriles of formula I, wherein X is CN. This hydrolysis may be accomplished in conventional manner e.g. by concentrated (e.g. 96%) sulphuric acid.

Thioamides of formula I wherein X is CSNH₂ may be prepared by treatment of a nitrile of formula I, wherein X is CN with H₂ S to give the unsubstituted thioamide wherein X is CSNH₂. Substituted thioamides may be obtained by conducting this reaction in the presence of a primary amine R³ NH₂ wherein R³ is lower alkyl. The H₂ S reaction can be carried out in a suitable solvent in the presence of a catalyst such as a tertiary amine e.g. a trialkylamine such as triethylamine.

The nitriles of formula I wherein X is CN, may be prepared by dehydration of the corresponding amides of formula I wherein X is CONH₂. Such dehydration can be carried out with P₂ O₅ as the dehydrating agent. Other dehydrating agents are phosphorus pentachloride or thionyl chloride. It has also been found that this decomposition can be effected with P₂ S₅ and this is believed to be a novel reaction per se. The decomposition with P₂ S₅ has been observed as a side reaction during the conversion of the amides of formula I wherein X is CONH₂ to the corresponding thioamides wherein X is CSNH₂ using P₂ S₅. The nitriles can either be separated, e.g. by chromatography or the mixture treated in situ with H₂ S for conversion of the nitrile to the corresponding thioamide. The dehydration may also be effected by heating the amide in hexamethylphosphorictriamide as solvent. When using this solvent it has been found that a compound of formula I in which X is CONMe₂ may be formed as a significant by-product. The latter is also believed to be a novel reaction per se.

A further method for preparing the thioamides of formula I, wherein X is CSNH₂ comprises reacting a nitrile of formula I wherein X is CN with a thioamide of formula R⁸ CSNH₂ is an alkyl group, e.g. a loweralkyl group of 1-6 carbon atoms, preferably a methyl group, in a suitable solvent such as dimethyl formamide saturated with hydrogen chloride.

The starting compounds of formula I wherein X is hydrogen, used in the above mentioned carboxylation reaction may be prepared by cyclisation of a compound of formula VI in the presence of hydroxylamine ##STR6## wherein R¹ and R² are as defined above but R¹ is preferably other than hydrogen and R⁶ and R⁷ are as defined above. Starting compounds of formula I, when X is hydrogen, R¹ is hydrogen and R⁷ is hydrogen, or if not hydrogen is not on the 5-position may be prepared by reduction of the corresponding 5-oxo compound (VII) using a reducing agent which does not affect the unsaturation of the fused pyridine ring e.g. hydrazine i.e. a Wolff-Kishner reduction. ##STR7##

The starting material of formula (VII) wherein R² and R⁶ are hydrogen may be prepared by the following scheme: ##STR8##

The reaction can be carried out in a suitable solvent e.g. dimethylformamide at room temperature followed by distillation of the products.

Compounds of formula I wherein X is hydrogen, R¹ is hydrogen and R² is other than hydrogen may be prepared by known methods.

The compounds of formula VI (wherein R⁷ is hydrogen or is not on both positions adjacent the oxo group) may be prepared by one of the following schemes: ##STR9## wherein R¹, R², R⁶, and R⁷ are as defined above, R¹ being other than hydrogen. The reactants used are known compounds or may be prepared by methods known for analogous compounds.

Other compounds for preparing starting compounds of formula I wherein X is hydrogen are described in the literature e.g. Breitmaier & Bayer Tetrahedron Letters No. 38, 1970, 3291-3294, which gives methods for preparing compounds in which X is hydrogen and R¹ and R² are hydrogen and X is hydrogen and R² is alkyl.

The following Examples illustrate the invention including preparation of precursor compounds for the nitriles of the invention and use of the nitriles in preparing thioamides; all temperatures are in ° C.

EXAMPLE 1

A. 2-phenyl-5,6,7,8-tetrahydroquinoline

2-(3'-Phenyl-3'-oxopropyl)cyclohexanone was prepared according to the method of W. Hahn and J. Epsztain (Roczniki Chem. 1963, 37, 403-12): A mixture of β-dimethylaminopropiophenone (27 gm.) and cyclohexanone (37.5 g.) were heated at reflux for 5 hours under nitrogen and the solvent removed in vacuo. The residual oil was distilled giving 2-(3'-phenyl-3'-oxopropyl)cyclohexanone (14 g.) which was cyclised to the title compound according to the method of Hahn and Epsztain by dissolving the diketone (12 g.) in ethanol (65 ml.), treating with hydroxylamine hydrochloride (9 g.) and heating under reflux for 1 hour. The cooled reaction mixture was poured onto water (300 ml.), extracted with ether (2 × 50 ml.) and the extracts discarded. The aqueous solution was made basic with K₂ CO₃ and extracted with ether (3 × 50 ml.). The combined ether extracts were dried and the solvent removed in vacuo. The residual oil was distilled to give the title compound as a colourless oil (7 g.) b.p. 134°-8° C/15 mm.

Found: C, 85.40; H, 7.5; N, 6.9%

C₁₅ h₁₅ n requires: C, 86.00; H, 7.2; N, 6.7%.

B. methyl-2-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxylate

A solution of 2-phenyl-5,6,7,8-tetrahydroquinoline (20 g.) in ether (50 ml.) was added dropwise over 30 mins. to a preformed ethereal solution of phenyllithium (prepared from bromobenzene (40 g.) and lithium (2.78 g.) in dry ether (160 ml.). The reaction mixture was stirred for 1 hour at room temperature and treated with dry CO₂ gas until the colour was discharged. The solvent was removed in vacuo and the residue dissolved in ethanol saturated with dry HCl gas (250 ml.) and the solid filtered and recrystallised from water giving 2-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxylic acid hydrochloride (12 g.). This was dissolved in methanol (200 ml.) and the solution treated with dry HCl gas whilst heating at reflux for 4 hours. The solvent was removed in vacuo and the residue dissolved in water (50 ml.), made basic with 2N NaOH and extracted into chloroform (3 × 100 ml.). The combined extracts were dried, evaporated to dryness and the residual solid recrystallised from petroleum ether giving the title compound as colourless needles (11 g.) mp 75° C. Found: C, 76.8; H, 6.5; N, 5.14; C₁₇ H₁₇ NO₂ requires: C, 76.4; H, 6.4; N, 5.2%.

EXAMPLE 2

2-phenyl-5,6,7,8-Tetrahydroquinoline-8-carboxamide.

Methyl-2-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxylate (4 g.) was dissolved in methanol previously saturated with ammonia (90 ml.) and heated in a bomb at 100° C for 4 days. Removal of the solvent in vacuo gave an oily solid which on recrystallisation from ethyl acetate gave the title compound as colourless needles (1.5 g.) mp 145° C. Found: C, 76.4; H, 6.5; N, 11.1% C₁₆ H₁₆ N₂ O requires: C, 76.2; H, 6.4; N, 11.1%.

EXAMPLE 3

2-phenyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

2-Phenyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (8 g.) was dissolved in pyridine (20 ml.), treated with P₂ S₅ (5.2 g.) and the mixture heated at reflux temperature for 30 minutes. The solvent was removed in vacuo and the residual oil dissolved in dilute HCl, washed with ether (2 × 50 ml.) and the washings discarded. The aqueous solution was made basic, extracted into chloroform (3 × 50 ml.) and the combined extracts dried and evaporated to dryness. The residual oil was chromatographed on silica gel by elution with chloroform giving 8-cyano-2-phenyl-5,6,7,8-tetrahydroquinoline (1.2 g.) as colourless needles from ether mpt. 100° C. Found: C, 82.0; H, 6.2; N, 11.7% C₁₆ H₁₄ N₂ requires: C, 82.0; H, 6.0; N, 11.9%. Further elution with chloroform gave the title compound (1.1 g.) as colourless needles from ether mpt. 154° C. Found: C, 71.8; H, 6.1; N, 10.2 %, C₁₆ H₁₆ N₂ S requires: C, 71.6; H, 6.0; N, 10.4%.

EXAMPLE 4

8-cyano-2-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxamide.

2-Phenyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (6 g.) was dissolved in hexamethylphosphorictriamide (24 ml.) and the solution heated at 220° C for 2 hours. The cooled reaction mixture was poured onto water (50 ml.), extracted with chloroform (3 × 100 ml.) and the combined extracts washed with water (3 × 100 ml.), dried and evaporated to dryness. The residual oil was chromatographed on silica gel by elution with chloroform giving 8-cyano-2-phenyl-5,6,7,8-tetrahydroquinoline (2.5 g.) recrystallised from ether as colourless needles mpt. 100° C. Further elution with chloroform gave N,N-dimethyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (1.1 g.) which recrystallised from ether as colourless needles mpt. 140° C. Found: C, 77.17; H, 7.22; N, 10.24%. C₁₈ H₂₀ N₂ O requires: C, 77.11; H, 7.19; N, 9.99%.

EXAMPLE 5

2-phenyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide.

2-Phenyl-8-cyano-5,6,7,8-tetrahydroquinoline (2 g.) was dissolved in pyridine (5 ml.) and triethylamine (1.3 ml.) and the solution treated with H₂ S gas for 6 hours and the reaction mixture allowed to stand at room temperature for 12 hours. The solvent was removed and the residual oil dissolved in dilute HCl, extracted with ether (2 × 50 ml.) and the extracts discarded. The aqueous solution was made basic and extracted into chloroform (3 × 50 ml.). The combined extracts were dried and evaporated in vacuo to give 2-phenyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide which was dissolved in ethanol (5 ml.), diluted with ether (25 ml.) and the solution saturated with HCl gas. The solvent was removed in vacuo and the residual solid recrystallised from methanol-ether giving hydrochloride of the title compound as colourless needles mpt. 211° C. Found: C, 63.41; H, 5.70; N, 8.94%. C₁₆ H₁₆ N₂ S. HCl requires: C, 63.04; H, 5.62; N, 9.19 %.

EXAMPLE 6

A. 5,6,7,8-tetrahydroquinoline

5-Oxo-5H-6,7,8-trihydroquinoline was prepared according to the method of F. Zymalkawski (Arch. Chem. 1961, 294, 759) by adding propiolaldehyde (16 g.) to a solution of 3-aminocyclohex-2-enone (31 g.) in DMF (150 ml.) over 5 mins. When the exothermic reaction had ceased, the flask was fitted for downward distillation and the reaction mixture heated at 100° C under a vacuum of 15 mm. and the distillate collected and discarded. The temperature was raised to 160°-170° collecting the distillate which was dissolved in dilute HCl (75 ml.) and extracted with ether (2 × 50 ml.). The combined ethereal extracts were discarded. The aqueous solution was made basic and extracted with ether (3 × 150 ml.) and the combined ethereal extracts dried and evaporated in vacuo. The residual oil was distilled giving 5-oxo-5H-6,7,8-trihydroquinoline (21 g.) b.p. 133°-4° C/15 mm. which was dissolved in diethylene glycol (190 ml.) and treated with hydrazine hydrate (14 g.) and sodium hydroxide (14 g.). The reaction mixture was heated at reflux for 30 minutes and then for 31/2 hours under a Dean and Stark water separator. The cooled reaction mixture was poured onto water (100 ml.), extracted with ether (3 × 100 ml.) and the combined extracts dried and evaporated in vacuo. The residual oil was distilled giving the title compound as a colourless oil (10 g.) b.p. 100°-5° C/15 mm.

B. methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

A solution of 5,6,7,8-tetrahydroquinoline (14 g.) in dry ether (100 ml.) was added dropwise over 1/2 hour to an ethereal solution of phenyl lithium (prepared from bromobenzene (42 g.) and lithium (3.7 g.) in dry ether (300 ml.) and the reaction mixture stirred at room temperature for a further one hour. The cooled reaction mixture was saturated with dry CO₂ gas, evaporated in vacuo and the residue treated with methanol previously saturated with dry HCl (500 ml.) and the solution heated at reflux for 12 hours. The solvent was removed in vacuo and the residue dissolved in water (50 ml.), extracted with ether (3 × 150 ml.) and the extracts discarded. The aqueous solution was made basic and extracted with ether (3 × 100 ml.). The combined ethereal extracts were dried, evaporated in vacuo and the residual oil distilled giving methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate as a colourless oil (13 g.) b.p. 92° C/0.05 mm. The hydrochloride was prepared by saturating an ethereal solution with dry HCl gas and recrystallising the resultant solid from methanol-ether to give the hydrochloride of the title compound as colourless needles mpt. 173° C. Found: C, 58.2; H, 6.3; N, 6.3%. C₁₁ H₁₃ NO₂.HCl requires C, 58.0; H, 6.2; N, 6.2%.

EXAMPLE 7

5,6,7,8-tetrahydroquinoline-8-carboxamide.

Methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate (9 g.) was dissolved in methanol previously saturated with ammonia (270 ml.) and heated in a bomb at 100° C for 5 days. The solvent was removed and the residual oil triturated with hot petroleum ether (40°-60°). The resultant solid was filtered and then recrystallised from ethylacetate giving the title compound as colourless needles mpt. 132° C (5 g.). Found: C, 67.7; H, 7.1; N, 16.0%. C₁₀ H₁₂ N₂ O requires: C, 68.1; H, 6.9; N, 15.9%.

EXAMPLE 8

5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

A solution of 5,6,7,8-tetrahydroquinoline-8-carboxamide (1.2 g.) in pyridine (15 ml.) was treated with P₂ S₅ (0.8 g.) and the mixture heated at reflux for 30 mins. The solvent was removed in vacuo and the residual oil treated with 2N NaOH (5 ml.) and saturated with solid K₂ CO₃ and extracted into chloroform (3 × 50 ml.). The combined extracts were dried and the solvent removed in vacuo. The residual oil (mainly 8-cyano-5,6,7,8-tetrahydroquinoline) was dissolved in pyridine (4 ml.) and triethylamine (1 ml.) and the solution saturated with H₂ S (6 hours) and allowed to stand over night. Removal of the solvent gave a solid (850 mgs.) which was recrystallised from methanol giving the title compound as the quarter hydrate, colourless needles m.p. 160° C. Found: C, 59.8; H, 6.2; N, 14.0 %. C₁₀ H₁₂ N₂ S.1/4 H₂ O requires: C, 59.6; H, 6.4; N, 13.9%.

The UV, IR and NMR Spectra of the title compound were determined:

    ______________________________________                                         1.  UV Spectrum in 95% EtOH (1.07 mg. in 100 ml.)                                  Max 272 nm, ε 13,300                                               2.  IR Spectrum                                                                    3230 cm.sup.-.sup.1                                                                        NH.sub.2 stretch                                                   3060 cm.sup.-.sup.1                                                            1660 cm.sup.-.sup.1                                                        NH.sub.2 deformation or/and C=CN stretch                                           1575 cm.sup.-.sup.1                                                                        C=C stretch                                                        1500-900 cm.sup.-.sup.1                                                                    `fingerprint region`; numerous bands                                           caused by complex and coupled vibrations.                                      Two bands are particularly prominent                                           1280 cm.sup.-.sup.1 and 1020 cm.sup.-.sup.1                        802 cm.sup.-.sup.1                                                         CH deformation, characteristic of 2,3-                                             720 cm.sup.-.sup.1                                                                         disubstituted pyridine.                                        3.  NMR Spectrum - in d.sub.6 DMSO (100 MH.sub.2)                                  δ 1.5 - 2.3                                                                          broad multiplet                                                                             4 protons                                                                             CH.sub.2 -6 and 7                              δ 2.7 multiplet    2 protons                                                                             CH.sub.2 -5                                    δ 4.15                                                                               triplet (J=7Hz)                                                                             1 proton                                                                              CH-8                                           δ 7.08                                                                               quartet      1 proton                                                                              H-3                                            δ 7.44                                                                               quartet      1 proton                                                                              H-4                                            δ 8.29                                                                               quartet      1 proton                                                                              H-2                                            δ 9.25 and 9.45                                                                      broad doublet                                                                               2 protons                                                                             NH.sub.2                                   ______________________________________                                    

It is indicated in the index to Chemical Abstracts that 5,6,7,8-tetrahydroquinoline-8-thiocarboxamide is disclosed in Z. Naturforch. 6b, 147-155 (1951), however, the actual abstract does not disclose the compound and examination of the paper reveals that the index is in error since the compound actually disclosed is 8-quinoline thiocarboxamide, the benzene ring of which has been shown without the unsaturation being marked in accordance with a custom then in use, see Organic Chemistry, Paul Karrer, 4th English Edition, Elsevier, 1950 eg. at page 813.

EXAMPLE 9

A. 2-t-Butyl-5,6,7,8-tetrahydroquinoline

5-Dimethylamino-2,2-dimethylpentan-3-one hydrochloride (100 g.), prepared from pinacolone according to the method of Casey & Ison (Tetrahedron, 1969, 25, 641-6) was dissolved in water (50 ml.) and the pH adjusted to 12.0 with 10N NaOH and extracted with ether (3 × 50 ml.). The combined ethereal extacts were dried (MgSO4), evaporated in vacuo and the residual oil dissolved in cyclohexanone (300 ml.). The mixture was heated at reflux temperature for 8 hours and then cooled. The reaction mixture was then distilled at 15 mm. to remove excess cyclohexanone and then at 1 mm. to give 2(3'-t-butyl-3'-oxopropyl)cyclohexanone (82 g.) which was dissolved in ehtanol (275 ml.) and treated with hydroxylamine hydrochloride (70 g.). The mixture was heated at reflux temperature for 2 hours as described in the general method of W. Hahn and J. Epsztain (Roczniki Chem. 1963, 37, 403-12). The solvent was removed in vacuo and the residual oil dissolved in ether (100 ml.). The ethereal solution was washed with dilute HCl (3 × 20 ml.) and discarded. The aqueous solution was made basic with 2N NaOH and extracted with ether (3 × 50 ml.) and the combined extracts dried and evaporated in vacuo. The residual oil was distilled giving the title compound as a colourless oil b.p. 80°-6° C/1 mm. (yield 47 g., 64%).

B. 2-t-Butyl-5,6,7,8-tetrahydroquinoline-8-carboxamide

Methyl-2-t-butyl-5,6,7,8-tetrahydroquinoline-8-carboxylate was prepared from 2-t-butyl-5,6,7,8-tetrahydroquinoline (18.9 g., 0.1 m). and phenyl lithium (0.1 m.) by the general method described in Example 1B and was isolated as a pale yellow oil (9 g.) b.p. 106° C/0.4 mm.

The title compound was prepared from methyl-2-t-butyl-5,6,7,8-tetrahydroquinoline-8-carboxylate (8 g.) by the general method described in Example 2 and was isolated as colourless needles (3 g.) after recrystallisation from n-hexane m.p. 131° C. Found: C, 72.06; H, 8.71; N, 11.62%. C₁₄ H₂₀ N₂ O requires: C, 72.38; H, 8.68; N, 12.06%.

EXAMPLE 10

2-t-Butyl-8-cyano-5,6,7,8-tetrahydroquinoline

The title compound may be prepared from 2-t-butyl-5,6,7,8-tetrahydroquinoline-8-carboxamide following the procedure described in Example 3.

EXAMPLE 11

5,6,7,8-tetrahydroquinoline

3-Methoxyacrolein was prepared from 1,1,3,3-tetramethoxypropane (Helv. Chim. Acta 1959, 42, 851) and converted to 3-aminoacrolein according to the method of Breitmaier and Gassenmann (Chem. Ber. 1971, 104, 665-7).

5,6,7,8-Tetrahydroquinoline was prepared from 3-aminoacrolein as described by Breitmaier and Bayer (Tet. Letts 1970, 38, 3291). A mixture of 3-aminoacrolein (7.3 gm, 0.1 m) and cyclohexanone (12 gm., 0.12m) was treated with triethylamine (5 ml.) and piperidinium acetate (0.1 gr) and the mixture heated in an oil bath at 120° for 24 hours. The cooled reaction mixture was dissolved in ether (100 ml.), washed with water and 2N HCl (2 × 20 ml.) and the acid washings combined, made basic with sodium carbonate and extracted with ether. The combined extracts were dried, evaporated and the residue distilled to give the title compound as a pale yellow oil (4.5 gm, 35%) b.p. 100°/15 mm.

EXAMPLE 12 2-Methyl-5,6,7,8-tetrahydroquinoline.

4-Diethylaminopropan-2-one prepared from acetone and diethylamine (J.C.S. 1937, 53) was reacted with cyclohexanone by the general method described in C.A. 72, 132478h to give 2(3¹ -methyl-3¹ -oxopropyl) cyclohexanone as a colourless oil b.p. 150°/20 mm.

The title compound was prepared from 2(3¹ -methyl-3¹ -oxopropyl)cyclohexanone according to the general method described in Examples 1 and 9A and isolated as a colourless oil b.p. 116°-20°/18 mm. (60% yield).

Example 13

2-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide

Reaction of 2-methyl-5,6,7,8-tetrahydroquinoline with phenyl lithium and carbon dioxide followed by esterification according to the general method described in Examples 1B and 6B gave an inseparable mixture of methyl-2-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate and methyl 5,6,7,8-tetrahydroquinoline-2-acetate which was converted without purification to a mixture of 2-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide and 5,6,7,8-tetrahydroquinoline-2-acetamide by reaction with ammonia using the method described in Example 2. Fractional recrystallisation from diisopropyl ether gave the title compound as colourless needles m.p. 114° (overall yield 30%) (Found: C, 69.31, H, 7.45, N, 14.7, C₁₁ H₁₄ N₂ O requires: C, 69.45, H, 7.42; N, 14.72%).

EXAMPLE 14

2-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

2-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide was treated with P₂ S₅ to give 2-methyl-8-cyano-5,6,7,8-tetrahydroquinoline which was treated with H₂ S (both reactions being carried out by a method described in Example 8 to give the title compound as colourless needles from ethylacetate (28%) m.p. 98° (Found: C, 64.32; H, 6.93; N, 13.52%, C₁₁ H₁₄ N₂ S requires: C, 64.04; H, 6.84; N, 13.58%).

EXAMPLE 15

3-methyl-5,6,7,8-tetrahydroquinoline

The title compound was prepared from commercially available 3-amino-2-methylacrolein and cyclohexanone according to the method of Breitmaier and Bayer (Tet. Letts, 1970, 38, 3291-4) and isolated as a pale yellow oil b.p. 120°/15 mm. (30% yield).

EXAMPLE 16

Methyl 3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate

The title compound was prepared from 3-methyl-5,6,7,8-tetrahydroquinoline according to the general method described in Example 1B and isolated as a pale yellow oil b.p. 120°/0.25 mm. (80% yield). The hydrochloride was prepared in the usual way (of Example 6B) and isolated as colourless needles from ethanol/ether m.p. 146° (Found: C, 59.9; H; 6.7; N, 6.0. C₁₂ H₁₅ NO₂ HCl requires: C, 59.60; H, 6.7; N, 5.8%).

EXAMPLE 17

3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide.

The title compound was prepared from methyl 3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate by the method described in Example 2 and was isolated as colourless needles from hexane m.p. 118° (50% yield) (Found: 69.60; H, 7.5; N, 14.8; C₁₁ H₁₄ N₂ O requires: C, 69.5; H, 7.4; N, 14.7%).

EXAMPLE 18

3-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

3-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide was treated with P₂ S₅ to give 3-methyl-8-cyano-5,6,7,8-tetrahydroquinoline which was treated with H₂ S as described in Example 8 giving the title compound as colourless needles from benzene m.p. 151° (50% yield) (Found: C, 63.71; H, 6.85; N, 13.38% C₁₁ H₁₄ N₂ S requires: C, 64.04; H, 6.84; N, 13.58%).

The hydrochloride was prepared by dissolving the title compound in the minimum amount of isopropanol and then adding a solution of ether saturated with dry HCl gas. The hydrochloride precipitated as colourless needles m.p. 219° (Found: C, 54.33; H, 6.23; N, 11.42% C₁₁ H₁₄ N₂ SHCl requires: C, 54.42; H, 6.23; N, 11.54%).

EXAMPLE 19

Methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

n-Butylbromide (285 ml.) in dry ether (500 ml.) was added to clean lithium wire (42 g., 6 m) in dry ether (1 l.) under nitrogen at such a rate to maintain an internal temperature of -15° C. Upon completion of the addition the reaction mixture was stirred until the temperature rose to 10° C (approx. 2 hours). The concentration of butyl lithium was calculated by standardising against N/10 HCl and the quantity of 3-methyl-5,6,7,8-tetrahydroquinoline required in the next stage adjusted to have a 1.2 m excess of butyl lithium.

A stirred solution of 3-methyl-5,6,7,8-tetrahydroquinoline (147 g., 1 m) in dry ether (700 ml.) was treated with a freshly prepared solution of butyl lithium (860 ml. of a 1.4 M solution i.e. 1.2 m) under nitrogen. The reaction mixture was stirred for an additional 15 min. and a slow stream of dry CO₂ gas bubbled into the reaction mixture until colourless. The reaction mixture was diluted with water (1.2 l), filtered and the aqueous phase separated and extracted with ether (3 × 500 ml). The combined ethereal extracts were processed to give a recovered 3-methyl-5,6,7,8-tetrahydroquinoline (40 g.) b.p. 116°-20°/15 mm.

The aqueous layer was evaporated to dryness and the residual solid treated with a solution of methanol previously saturated with dry HCl gas (1.5 l) and allowed to stand at room temperature for 12 hours. The volatiles were removed in vacuo. The residual oil was redissolved in water (1 l.), extracted with ether (3 × 250 ml.) and the extracts discarded. The aqueous solution was adjusted to pH 9.0 with Na₂ CO₃ and extracted with ether (4 × 250 ml.). The combined extracts were dried and the solvent removed in vacuo to give the title compound as a pale yellow oil (85 g. 42%) GLC (10% SE30, T = 200°) R₁ = 3.25 min, 93% pure.

EXAMPLE 20

Methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

A solution of 3-methyl-5,6,7,8-tetrahydroquinoline (5 g., 0.034 m) in dry ether (50 ml.) was treated portionwise with a solution of butyl lithium in hexane (0.04 m) under nitrogen and the mixture allowed to stand at room temperature for 30 minutes. A slow stream of CO₂ gas was bubbled in until the reaction mixture was colourless. A further 0.02 m. of butyl lithium in hexane solution was added. The mixture was allowed to stand for 30 minutes and then treated with dry CO₂ gas as above. The reaction mixture was diluted with water (20 ml.), the aqueous layer extracted with ether (3 × 50 ml.) and the combined extracts retained for recovery of unreacted 3-methyl-5,6,7,8-tetrahydroquinoline. The aqueous phase was evaporated to dryness in vacuo. The resultant solid was treated with methanol previously saturated with dry HCl gas (50 ml.) and allowed to stand at room temperature for 3 hours. The solvent was removed and the residual oil dissolved in water (20 ml.) and extracted with ether (3 × 25 ml.) and the extracts discarded. The aqueous phase was adjusted to pH 9.0 with Na₂ CO₃ and extracted into ether (3 × 50 ml.). The combined extracts were dried and evaporated in vacuo to give the title compound as a colourless oil (4.3 g., 60%) GLC (10% SE30, T = 200°). R₁ = 3.25 min. 98% pure.

EXAMPLE 21

3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide.

A mixture of methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate (25 g., 0.13 m), formamide (11.6, 0.26 m) and sodium methoxide (from 2.99 g., 0.13m sodium) was heated with stirring in an oil bath at 120° for 1 hour. The reaction mixture was further heated at 100° for 3 hours under reduced pressure (15 mm Hg). The cooled reaction mixture was diluted with 2N HCl to give an acidic solution which was extracted with ethylacetate (2 × 50 ml.) and the combined extracts discarded. The aqueous solution was adjusted to pH 9.0 with solid Na₂ CO₃, saturated with NaCl and extracted with chloroform (3 × 100 ml.). The combined extracts were dried and evaporated to give a pale yellow oil which solidified on trituration with n-hexane. Recrystallisation from ethylacetate gave the title compound as colourless cubes (18.6 g., 88%) m.p. 110°. Found: C, 69.6; H, 7.4; N, 14.4%. C₁₁ H.sub. 14 N₂ O requires: C, 69.5; H, 7.4; N, 14.7%.

EXAMPLE 22

3-methyl-5,6,7,8-Tetrahydroquinoline-8-carboxamide.

A mixture of methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate (25 g. 0.13 m), formamide (11.6 g., 0.26 m) and sodium methoxide (from 2.99 g., 0.13 m sodium) was heated on a steam bath for 1 hour while bubbling nitrogen through the mixture, to blow off the methyl formate produced in the reaction. The cooled reaction mixture was diluted with 2N HCl and worked up as described in Example 21 to give the title compound in 90% yield.

EXAMPLE 23

3-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide.

A solution of 3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (27.9 g. 0.14 m) in dry pyridine (300 ml.), saturated with H₂ S gas, was treated with P₂ S₅ (26 g., 0.14 m) and heated at reflux for 45 min. whilst maintaining a slow stream of H₂ S gas. The reaction mixture was evaporated to dryness in vacuo and cooled to 0° C, made alkaline with 10% sodium hydroxide and the solution extracted with chloroform (3 × 100 ml.). The combined extracts were washed with brine, dried and evaporated in vacuo. The residual oil was triturated with benzene and the solid filtered and recrystallised from benzene to give the title compound as pale yellow needles m.p. 149° (21.8 g., 87%). The hydrochloride was prepared as already described in Example 18 and isolated as colourless needles m.p. 219° C.

EXAMPLE 24

Methyl 3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

Charge a 3-necked flask with 3-methyl-5,6,7,8-tetrahydroquinoline (45 g. 0.29 moles) and ether (400 ml.). Stir. Add phenyl lithium solution (330 ml. of a 1 molar solution 0.3 moles in ether) at a rate to give gentle reflux. Maintain reflux for 2 hours. Cool in an ice-bath and bubble CO₂ through solution till no further change. Add water (700 ml.) to dissolve solid. Separate and wash aqueous layer with ether (3 times). Evaporate aqueous layer to dryness in vacuo. To the residue add a saturated solution (1 liter) of methanolic HCl and stand overnight at room temperature. Evaporate to dryness in vacuo and dissolve residue in water. Wash water with ether (3 times). Basify aqueous solution with solid sodium carbonate and extract with ether (a heavy white solid also precipitates, but this does not interfere with the extraction). Wash ether layer with water, then brine. Dry and evaporate. Yield 25 g. (44%). GLC = 88% pure.

EXAMPLE 25

Methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

A solution of 15% n-butyl lithium in hexane (51 ml. ca. 0.12 m) was added portionwise to a solution of 3-methyl-5,6,7,8-tetrahydroquinoline (14.7 g., 0.1 m) in ether (100 ml.) and the mixture allowed to stand at room temperature for 1 hour and then added dropwise to a cooled, stirred solution of methylchloroformate (9.45 g., 0.1 m) in ether (100 ml.). The mixture was stirred at 50° C for 1 hour. The reaction mixture was diluted with water (20 ml.) and then treated with 2N HCl until acidic. The ethereal solution was separated and washed with 2N HCl (2 × 25 ml). The combined aqueous washings were extracted with ether and the ethereal extracts discarded. The aqueous solution was adjusted to pH 9.0 with Na₂ CO₃ and extracted with chloroform (3 × 50 ml.) and the combined extracts dried and evaporated to give a pale yellow oil (16 g) which on GLC examination (3% SE30) showed a mixture of unreacted tetrahydroquinoline (45%), the title compound (23%) and the 8,8-dicarboxylic ester (20%). The mixture was treated with 10% sodium hydroxide (75ml.). and heated at reflux with stirring for 4 hours, cooled and extracted with ether (3 × 50 ml.) The combined ethereal extracts were dried, evaporated and distilled to give unreacted 3-methyl-5,6,7,8-tetrahydroquinoline (7 g.) b.p. 116°/18 mm Hg. The basic solution was adjusted to pH 8.5-9.0 with concentrated HCl and evaporated to dryness and the residue treated with methanol previously saturated with dry HCl (50 ml.) and allowed to stand at room temperature for 5 hours. The solvent was removed and the residue dissolved in water (20 ml.) and extracted with ether (2 × 50 ml.). The aqueous solution was adjusted to pH 9.0 with Na₂ CO₃ and extracted with chloroform (3 × 25 ml.) and the combined extracts dried and evaporated to give the title compound (3 gm.).

EXAMPLE 26

3-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide hydrochloride.

Crystal Form A

3-Methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide (1 g.) prepared as described in Example 18 was dissolved in boiling isopropylalcohol (25 ml.), filtered and allowed to cool to 40° C. An excess of an ethereal solution of hydrogen chloride was added followed by sufficient ether to cause turbidity. On cooling the title compound was isolated as fine colourless needles (0.95 g.) mpt 244° C. Found: C, 54.3; H, 6.2; N, 11.4%. C₁₁ H₁₄ N₂ S.HCl requires C, 54.4; H, 6.2; N, 11.5%. I.R. ν_(max).sup. Nujol Mull 3300 (shoulder), 3230 (broad), 3060 (broad), 2540 (broad), 1650 (strong), 1605, 1555 cm.sup.⁻¹. This I.R. Spectrum was identical with that exhibited by the product of Example 18.

Crystal Form B

3-Methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide (1 g.) prepared as described in Example 18 was dissolved in boiling isopropyl alcohol (15 ml.) and a slight excess of an ethereal solution of hydrogen chloride added without cooling. The title compound was obtained as fine colourless needles (950 mg) m.p. 244° C. Found: C, 54.58; H, 6.29; N, 11.34%. C₁₁ H₁₄ N₂ S.HCl requires C, 54.42; H, 6.23; N, 11.54%. I.R. ν_(max) ^(Nujol) mull 3260 (broad), 3220 (broad), 3050, 2630 (broad), 1655-1630 (3 sharp bands), 1555cm.sup.⁻¹.

Crystal Form B - Alternative Method.

3-Methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide (0.5 g.) was dissolved in methanol (1 ml.) and treated with methanol saturated with hydrogen chloride (1 ml.) and the solution heated to boiling. Ethyl acetate was added, whilst the methanol evaporated, until turbid. On cooling the title compound was isolated as fine colourless needles (0.4 g.) m.p. 244°. Found: C, 54.11; H, 6.18; N, 11.31%. C₁₁ H₁₄ N₂ S.HCl requires: C, 54.42; H, 6.23; N, 11.54%. Crystal Form A could not be converted into crystal form By by crystallising from isopropylalcohol/ether or methanol/ethyl acetate.

Form A on standing for 2-3 days reverted to Form B. Form A could also be converted to Form B by heating at 40° C under vacuum for 6 hours.

EXAMPLE 27

3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide.

Crystal Form A

3-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (1 g.) prepared as described in Example 17 was dissolved in boiling di-isopropyl ether (80 ml.), filtered and allowed to cool. The title compound was isolated as fine colourless cubes (0.85 g.), m.p. 118° C. Found: C, 69.6; H, 7.5; N, 14.8%. C₁₁ H₁₄ N₂ O requires C, 69.5; H, 7.4; N, 14.7%. I.R. ν_(max) ^(nujol) 3395, 3195, 1650 (strong), 1620, 1605 (shoulder), 1595, 1560, 1235, 875 (strong), 620 (strong) cm.sup.⁻¹. The I.R. Spectrum was identical with that of the product of Example 17.

Crystal Form B.

3-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (1 g.) prepared as described in Example 17 was dissolved in boiling ethyl acetate (2 ml.), filtered and allowed to cool. The title compound was isolated as colourless rhombic crystals (0.80 g.) m.p. 113°. Found: C, 68.81; H, 7.40; N, 14.45%. C₁₁ H₁₄ N₂ O requires C, 69.50; H, 7.40; N, 14.70%. I.R. ν_(max) ^(nujol) 3395, 3280, 3185, 1680 (strong) 1605, 1595, 1560, 900 (strong), 575 (strong) cm.sup.⁻¹.

The crystal forms A and B can be interconverted by crystallisation from the appropriate solvents. Thus crystallisation of form A from ethyl acetate will give form B and crystallisation of form B from di-isopropyl ether will give form A.

EXAMPLE 28

Sym. Octahydroacridine-4-thiocarboxamide

Sym. octahydroacridine was prepared by converting cyclohexanone to di-(2-oxo-cyclohex-1-yl)-methane and further reacting with hydroxylamine according to the method of Gill et al (JACS 1952, 74, 4923) and was isolated as a colourless oil b.p. 110°-15°/0.5 mm. in 40% overall yield.

A solution of sym octahydroacridine (5 gm. 0.026 m.) in dry ether (50 ml.) was treated dropwise with a 15% solution of butyl lithium in hexane (11 ml. 0.026 m.) and the mixture stirred at room temperature for 15 min. under an atmosphere of nitrogen. The nitrogen was replaced by CO₂ gas which was bubbled through the reaction mixture until colourless. The reaction mixture was diluted with water (50 ml.) and the organic layer separated and the aqueous phase extracted with ether (2 × 50 ml.). The combined extracts were retained for recovery of sym. octahydroacridine. The aqueous phase was evaporated to dryness, the residue treated with methanol previously saturated with dry HCl (50 ml.) and the solution allowed to stand at room temperature for 3 hours. The solvent was removed in vacuo the residue diluted with water (20 ml.) and extracted with ether. The aqueous phase was adjusted to pH 10. with solid Na₂ CO₃ and extracted with ether (3 × 20 ml.). The combined extracts were washed with brine, dried and evaporated to give methyl-sym. octahydroacridine-4-carboxylate. (1 gm. 15%).

A solution of methyl-sym octahydroacridine-4-carboxylate (5 gm) in methanol previously saturated with ammonia (80 ml.) was heated at 140° for 3 days in a stainless steel bomb. The solvent was removed and the residual solid recrystallised from di-isopropyl ether to give sym. octahydroacridine-4-carboxamide as colourless needles (2.6 g, 57%) m.p. 159° (Found: C, 72.98; H, 8.04; N, 12.01%. C₁₄ H₁₈ N₂ O requires: C, 73.01; H; 7.88; N, 12.17%).

A solution of sym. octahydroacridine-4-carboxamide (1.8 gm.) in pyridine (17 ml.) was treated with hydrogen sulphide for 5 mins. The reaction mixture was treated with phosphorus pentasulphide (1.4 g.) and heated at reflux for 45 mins maintaining a slow stream of hydrogen sulphide throughout. The cooled reaction mixture was evaporated and the residue treated with 10% sodium hydroxide until alkaline. The aqueous solution was extracted with chloroform (3 × 50 ml.) and the combined extracts washed with brine, dried and evaporated and the residual solid recrystallised from di-isopropyl ether giving the title compound as a pale yellow powder (0.3 g. 16%) m.p. 104°-6° (solidifies and remelts at 148°). (Found: C, 68.69; H, 7.54; N, 10.98%. C₁₄ H₁₈ N₂ S requires: C, 68.26; H, 7.36; N, 11.37%).

EXAMPLE 29

3-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

3-Methyl-8-cyano-5,6,7,8-tetrahydroquinoline (1.7 g., 0.01 m.) and thioacetamide (1.5 g., 0.02 m.) were dissolved in dimethylformamide (50 ml.), the solution saturated with dry hydrogen chloride gas and then heated on a steam bath for 4 hours. The cooled reaction mixture was poured onto water (200 ml.), washed with ethyl acetate (2 × 200 ml.) and the extracts discarded. The aqueous solution was adjusted to pH 10.0 with 46% sodium hydroxide and extracted into methylene chloride (2 × 200 ml.). The combined extracts were dried (sodium sulphate), evaporated in vacuo and the residual oil triturated with isopropanol and filtered. Recrystallisation from benzene gave the title compound as pale yellow needles (1.3 g., 63%) m.p. 149°.

EXAMPLE 30

Methyl-3,7,7-trimethyl-5,6,7,8-tetrahydroquinoline-8-carboxylate

3,7,7-Trimethyl-5,6,7,8-tetrahydroquinoline (17.5 g., 0.1 m.) was dissolved in dry ether (200 ml.) and treated with a solution of n-butyl lithium in hexane (15% solution, 56 ml.) under nitrogen. The reaction mixture was allowed to stand at room temperature for 30 minutes and then treated with CO₂ gas until the intense red colour was discharged. The solvent was removed and the residual oily solid dissolved in water (20 ml.) then extracted with ether (3 × 50 ml.). The ethereal extracts were retained to recover unreacted starting material. The aqueous solution was evaporated to dryness, the residue treated with methanol previously saturated with dry HCl (100 ml.) and the solution allowed to stand at room temperature for 8 hours. The solvent was removed and the residual oil dissolved in water (50 ml.) and extracted with ether (3 × 50 ml.) and the extracts discarded. The aqueous solution was adjusted to pH 9.0 with sodium carbonate and extracted with ether (3 × 50 ml.). The combined extracts were dried and evaporated in vacuo to give the title compound as a pale yellow oil (1.8 g., 10%) I.R. Spectrum ν_(max) ^(film) 1748, 1570, 1460, 1160, 1030 cm.sup.⁻¹. GLC: R_(T) =3.1/2 min. (F11, 2% OV17, T = 150°).

The picrate of the title compound was formed by dissolving the free base (100 mg.) in ethanol (1 ml.) and adding a saturated solution of picric acid in ethanol (5 ml.) and allowing the picrate to crystallise. The picrate was removed by filtration, dissolved in the minimum volume of ethanol and precipitated by adding ether giving yellow needles m.p. 95°-7°. Analysis Found: c, 50.2; H, 4.7; N, 12.1% C₁₄ H₁₉ NO₂ picrate 3/4 H₂ O requires: C, 50.5; H, 5,0; N, 11.8%.

EXAMPLE 31

8-cyano-5,6,7,8-tetrahydroquinoline

5,6,7,8-Tetrahydroquinoline-8-carboxamide (2 g.) was refluxed and stirred with P₂ S₅ (1.4 g.) in pyridine 25 ml. for three hours. The mixture was evaporated to dryness in vacuo and then dilute sodium hydroxide was added to the residue followed by solid potassium carbonate. The product was extracted into chloroform and the chloroform extract washed with water and dried over MgSO₄. The dried extract was evaporated to dryness and the residue purified using column chromatography on silica gel with benzene/ethyl acetate (4:1) as eluent. The nitrile was dissolved in ethanol/ether and ethereal HCl added. The solution was evaporated to dryness giving the hydrochloride of the title compound as the quarter hydrate 800 mg. m.p. 185° C dec.

Analysis Found: C, 60.8; H, 5.7; N, 14.0% C₁₀ H₁₀ N₂ HCl 1/4 H₂ O requires C, 60.5; H, 5.8; N, 14.10%.

EXAMPLE 32

8-cyano-3-Methyl-5,6,7,8-tetrahydroquinoline

3-Methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide (3.6 g.) in pyridine (54 ml.) was treated with P₂ S₅ (7.56 g.) and the mixtures heated at reflux with stirring for 3 hours. The solvent was removed under reduced pressure and the residue cooled in ice-water then made basic with 10% NaOH. The basic solution was extracted with chloroform (3 times) and the combined extracts extracted with 2NHCl (twice). The combined acid extracts were basified with solid sodium carbonate and extracted into chloroform (3 times). The combined chloroform extracts were washed with brine dried (MgSO₄) and evaporated to give the title compound 1.7 g. This was converted to the hydrochloride by dissolving in ether and adding ethereal HCl. An oily residue was formed from which the supernatent liquid was decanted. The residue was triturated twice with dry ether and the remaining solid recrystallised from isopropyl alcohol giving the hydrochloride of the title compound m.p. 189° C. Analysis Found: C, 63.08; H, 6.26; N, 13.34% C₁₁ H₁₂ N.sub. 2 HCl requires: C, 63.30; H, 6.28; N, 13.43%.

EXAMPLE 33

2-phenyl-4(4'-methoxyphenyl)-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

A hot solution of sodium hydroxide [15 g. in water (15 ml.)] is added to a solution of 1-phenyl-3-(4'-methoxyphenyl)prop-2-enone (10.7 g. 0.045 mol.) and cyclohexanone (20 g. 0.2 mol.) in ethanol (150 ml.) at 40° C and the mixture stirred at room temperature for 12 hours. The reaction mixture is diluted with water (200 ml.) and the resultant solid filtered, dried and recrystallised from ethanol to give 2-[β-benzoyl-α-(4'-methoxyphenylethyl)]cyclohexanone as colourless needles m.p. 148° C (Found: C, 79.0, H. 7.4 C₂₂ H₂₄ O₃ requires: C, 78.5; H, 7.2%).

A solution of 2-[β-benzoyl-α-(4'-methoxyphenylethyl)] cyclohexanone (7.6. 0.021 mol.) in ethanol (25 ml.) is treated with hydroxylamine hydrochloride (3.42 g., 0.05 mol.) and the mixture heated at reflux with stirring for 2 hours. The cooled reaction mixture is diluted with water (50 ml.) and the pH adjusted to 1.0 with conc.HCl and extracted with ether (2 × 50 ml.) and the extracts discarded. The aqueous solution is adjusted to pH 9.0 with Na₂ CO₃ and extracted with ether (2 × 50 ml.) and the combined extracts washed with brine, dried (MgSO₄) and evaporated to give 2-phenyl-4(4'-methoxyphenyl)-5,6,7,8-tetrahydroquinoline as a colourless oil (5.8 g.) which is converted into methyl-2-phenyl-4(4'-methoxyphenyl)-5,6,7,8-tetrahydroquinoline-8-carboxylate following the method described in Example 19. The ester is converted into 2-phenyl-4(4'-methoxyphenyl)-5,6,7,8-tetrahydroquinoline-8-carboxamide following the method described in Example 22. The amide is converted into the title compound following the method described in Example 23.

EXAMPLE 34

3,8-dimethyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

3,8-dimethyl-8-cyano-5,6,7,8-tetrahydroquinoline is treated with H₂ S in pyridine in the presence of triethylamine following the general procedure of Example 5 and the title compound is isolated and recrystallised from benzene as the quarter hydrate, colourless meedles m.p. 164° C. This was converted to the hydrochloride by treatment in isopropanol with a solution of dry HCl gas in ether. The title compound hydrochloride crystallised as colourless needles m.p. 277° C.

EXAMPLE 35

4-methyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

Following the general procedures of Example 19 22 and 23 4-methyl-5,6,7,8-tetrahydroquinoline is converted to the title compound, which is obtained as the hydrochloride, colourless needles m.p. 213° C.

EXAMPLE 36

3,7,7-trimethyl-5,6,7,8-tetrahydroquinoline-thiocarboxamide

Methyl-3,7,7-trimethyl-5,6,7,8-tetrahydroquinoline-8-carboxylate obtained as described in Example 36 is converted to the 8-carboxamide following the general procedure of Example 22. The product is treated with phosphorus pentasulphide and H₂ S in pyridine following the general procedure of Example 23 to give the title compound which is converted to the hydrochloride. The hydrochloride of the title compound is recrystallised from isopropanol as a 1.1/4 hydrate m.p. 162° C.

Example 37

5,6,7,8-Tetrahydro-2,3-dihydro-1H-cyclopenta[b]quinoline-5-thiocarboxamide

2-(oxo-cyclopentyl)methyl cyclohexanone is prepared from 2-(dimethylaminomethyl)-cyclohexanone and cyclopentanone according to the method described in Ann. Chim. 1963, 53 (6), 819 and is isolated as a colourless oil in 80% yield b.p. 92° /0.05 mm.

5,6,7,8-Tetrahydro-2,3-dihydro-1H-cyclopenta[b]quinoline is prepared from 2-(2-oxocyclopentyl)methylacyclohexanone according to the method described in Ann.Chim., 1963, 53, (6), 819 and is isolated in 65% yield as a colourless oil b.p. 80°/0.05 mm. The hydrochloride is prepared for characterisation by treating an ethereal solution of the base with ethereal HCl and is isolated as the hemihydrate as colourless needles from ethanol-ether m.p. 104° C (Found: C, 65.7; H, 7.8; N, 6.6. C₁₂ H₁₆ N.HCl.1/2H₂ O requires: C, 65.8; H, 7.8; N, 6 4% 5,6,7,8-Tetrahydro-2,3-dihydro-1H-cyclopenta[b]-quinoline is converted to methyl 5,6,7,8-tetrahydro-2,3-dihydro-1H-cyclopenta[b]quinoline-5-carboxylate following the method described in Example 19 and this is converted to 5,6,7,8-tetrahydro-2,3-dihydro-1H-cyclopenta[b]-quinoline-5-carboxamide following the method described in Example 22. The amide is converted to the title compound, following the procedure of Example 23, and is recrystallised from isopropanol, dissolved in ether and treated with an excess of ethereal HCl. The resultant solid is recrystallised from ethanol-ether to give the hydrochloride of the title compound as the monohydrate m.p. 118° C. (Found: C, 54.6; H, 6.3; N, 10.0. C₁₃ H₁₆ S.HCl H₂ O requires: C, 54.5; H, 6.6; N, 9.8%)

EXAMPLE 38

3-trifluoromethyl-5,6,7,8-Tetrahydroquinoline-8-thiocarboxamide

3-Trifluoromethyl-5,6,7,8-tetrahydroquinoline (1 mol) is converted to methyl 3-trifluoromethyl-5,6,7,8-tetrahydroquinoline-8-carboxylate by treatment with 1.2 mol n-butyl lithium (prepared from n-butyl-bromide and lithium wire) in dry ether under nitrogen, the reaction mixture being stirred for 15 min. when a slow stream of dry CO₂ gas is bubbled into the reaction mixture until colourless. The reaction mixture is diluted with water, filtered, and the aqueous phase separated and extracted with ether. The aqueous layer is evaporated to dryness and the residual solid litherium 3-trifluoromethyl-5,6,7,8-tetrahydroquinoline-8-carboxylate is treated with a solution of methanol previously saturated with dry HCl gas and allowed to stand for 12 hours at room temperature. The volatiles are removed in vacuo and the residual oil is redissolved in water and extracted with ether. The aqueous phase is adjusted to pH9 with sodium carbonate and extracted with ether (4 times). The combined ether extracts are dried and the solvent evaporated in vacuo to leave methyl 3-trifluoromethyl-5,6,7,8-tetrahydroquinoline-8-carboxylate.

The carboxylate (1 mol) is heated with formamide (2 mols) and sodium methoxide (1 mol) on a steam bath for 1 hour while bubbling nitrogen through the mixture to blow off methyl formate produced in the reaction. The cooled reaction mixture is diluted with 2NHCl to give an acidic solution which is extracted with ethylacetate.

The aqueous phase is adjusted to pH 9 with solid sodium carbonate, saturated with sodium chloride and extracted with chloroform (3 times). The chloroform extracts are dried and evaporated to leave 3-trifluoromethyl-5,6,7,8-tetrahydroquinoline-8-carboxamide which is recrystallised from ethyl acetate.

The amide (1 mol) is dissolved in dry pyridine saturated with H₂ S gas and treated with P₂ S₅ (1 mol) then heated at reflux for 45 min. while maintaining a slow stream of H₂ S gas. The reaction mixture is evaporated to dryness in vacuo and cooled to 0° C, made alkaline with 10% sodium hydroxide and the solution extracted with chloroform (3 times). The combined extracts are washed with brine, dried and evaporated in vacuo to give the title compound.

EXAMPLE 39

3-phenyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

3-phenyl-5,6,7,8-tetrahydroquinoline is converted into methyl-3-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxylate following the procedure described in Example 19. The ester is converted into 3-phenyl-5,6,7,8-tetrahydroquinoline-8-carboxamide by the method described in Example 22. The amide is converted into the title compound by the method described in Example 23.

Replacing 3-phenyl-5,6,7,8-tetrahydroquinoline by each of the following starting materials in the above-mentioned procedure the following compounds are prepared:

    __________________________________________________________________________     Starting material                                                                               End Product                                                   __________________________________________________________________________     3-p-tolyl-5,6,7,8-tetrahydro-                                                                   3-p-tolyl-5,6,7,8-tetrhydro-                                  quinoline        quinoline-8-thiocarboxamide                                   3-o-chlorophenyl-5,6,7,8-                                                                       3-o-chlorophenyl-5,6,7,8-tetra-                               tetrahydroquinoline                                                                             hydroquinoline-8-thiocarbox-                                                   amide                                                         3-p-nitrophenyl-5,6,7,8-                                                                        3-p-nitrophenyl-5,6,7,8-tetra-                                tetrahydroquinoline                                                                             hydroquinoline-8-thiocarbox-                                                   amide                                                         3-p-trifluoromethylphenyl-                                                                      3-p-trifluoromethylphenyl-5,6,                                5,6,7,8-tetrahydroquinoline                                                                     7,8-tetrahydroquinoline-8-                                                     thiocarboxamide                                               3-p-methoxyphenyl-5,6,7,8-                                                                      3-p-methoxy-phenyl-5,6,7,                                     tetrahydroquinoline                                                                             8-tetrahydroquinoline-8-                                                       thiocarboxamide                                               __________________________________________________________________________

EXAMPLE 40

3-benzyl-5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

3-Benzyl-5,6,7,8-tetrahydroquinoline is converted into methyl-3-benzyl-5,6,7,8-tetrahydroquinoline-8-carboxylate by the method described in Example 19. The ester is converted into 3-benzyl-5,6,7,8-tetrahydroquinoline-8-carboxamide by the method described in Example 22. The title compound is prepared from the amide by the method described in Example 23.

EXAMPLE 41

Following the procedure of Example 19 but substituting the indicated starting materials for 3-methyl-5,6,7,8-tetrahydroquinoline the indicated end products are obtained.

    __________________________________________________________________________     Starting Material                                                                             End Product                                                     __________________________________________________________________________     4-trifluoromethyl-THQ                                                                         methyl-4-trifluoromethyl                                                       THQ-8-carboxylate                                               3-n-butyl-THQ  methyl-3-n-butyl-THQ-                                                          8-carboxylate                                                   3-n-pentyl-THQ methyl-3-n-pentyl-                                                             THQ-8-carboxylate                                               2-phenethyl-THQ                                                                               methyl-2-phenethyl-THQ-                                                        8-carboxylate                                                   3-benzyl-THQ   methyl-3-benzyl-THQ-                                                           8-carboxylate                                                   3-phenpropyl-THQ                                                                              methyl-3-phenpropyl-THQ-                                                       8-carboxylate                                                   4-benzyl-THQ   methyl-4-benzyl-THQ-8-                                                         carboxylate                                                     4-phenpropyl-THQ                                                                              methyl-4-phenpropyl-THQ-                                                       8-carboxylate                                                   3,5-dimethyl-THQ                                                                              methyl-3,5-dimethyl-THQ-                                                       8-carboxylate                                                   3,6-dimethyl-THQ                                                                              methyl-3,6-dimethyl-THQ-                                                       8-carboxylate                                                   3,7-dimethyl-THQ                                                                              methyl-3,7-dimethyl-THQ-                                                       8-carboxylate                                                   3-methyl-5-n-butyl-THQ                                                                        methyl-3-methyl-5-n-butyl-                                                     THQ-8-carboxylate                                               3-methyl-6-iso-propyl-THQ                                                                     methyl-3-methyl-6-iso-propyl-                                                  THQ-8-carboxylate                                               4-n-hexyl-THQ  methyl-4-n-hexyl-THQ-                                                          8-carboxylate                                                   5-methyl-THQ   methyl-5-methyl-THQ-8-carboxylate                               6-ethyl-THQ    methyl-6-ethyl-THQ-8-carboxylate                                7-n-propyl-THQ methyl-7-n-propyl-THQ-8-                                                       carboxylate                                                     5-phenethyl-THQ                                                                               methyl-5-phenethyl-THQ-8-                                                      carboxylate                                                     6-phenpropyl-THQ                                                                              methyl-6-phenpropyl-THQ-8-                                                     carboxylate                                                     __________________________________________________________________________

EXAMPLE 42

Following the procedure of Example 22 but replacing methyl-3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxylate with each of the methyl ester products of Example 41 the following amides are obtained,

5,6,7,8-tetrahydroquinoline(THQ)derivative

4-trifluoromethyl-THQ-8-carboxamide

3-n-butyl-THQ-8-carboxamide

4-n-hexyl-THQ-8-carboxamide

3-n-pentyl-THQ-8-carboxamide

2-phenethyl-THQ-8-carboxamide

3-benzyl-THQ-8-carboxamide

3-phenpropyl-THQ-8-carboxamide

4-benzyl-THQ-8-carboxamide

4-phenpropyl-THQ-8-carboxamide

3,5-dimethyl-THQ-8-carboxamide

3,6-dimethyl-THQ-8-carboxamide

3,7-dimethyl-THQ-8-carboxamide

3-methyl-5-n-butyl-THQ-8-carboxamide

3-methyl-6-isopropyl-THQ-8-carboxamide

5-methyl-THQ-8-carboxamide

6-ethyl-THQ-8-carboxamide

7-n-propyl-THQ-8-carboxamide

5-phenethyl-THQ-8-carboxamide

6-phenpropyl-THQ-8-carboxamide

EXAMPLE 43

Following the procedure of Example 23 but replacing 3-methyl-5,6,7,8-tetrahydroquinoline-8-carboxamide with each of the amide products of Example 42 the following thioamides are obtained:

Substituent(s) -5,6,7,8-tetrahydroquinoline-8-thiocarboxamide

4-trifluoromethyl-

3-n-butyl-

4-n-hexyl-

3-n-pentyl-

2-phenethyl-

3-benzyl-

3-phenpropyl-

4-benzyl-

4-phenpropyl-

3,5-dimethyl-

3,6-dimethyl-

3,7-dimethyl-

3-methyl-5-n-butyl-

3-methyl-6-isopropyl

5-methyl-

6-ethyl-

7-n-propyl-

5-phenethyl-

6-phenpropyl- 

We claim:
 1. A compound of formula IA ##STR10## and acid addition salts thereof with pharmaceutically acceptable acids, wherein R¹, R² and R⁶ are the same or different and are selected from hydrogen, trifluoromethyl, alkyl having from 1 to 6 carbon atoms, phenylalkyl wherein the alkyl group has 1 - 6 carbon atoms, or phenyl groups or R¹ and R² taken together represent a polymethylene chain of 3 to 5 carbon atoms, R⁷ represents hydrogen or from 1 to 3 groups selected from alkyl of 1 to 6 carbon atoms (which may be substituted by alkoxy of 1 to 6 carbon atoms or trifluoromethyl), phenylalkyl wherein the alkyl group has 1 to 6 carbon atoms and phenyl groups, and any of the phenyl or the phenyl portion of any phenylalkyl groups R¹, R², R⁶ and R⁷ may be substituted by alkyl of 1 to 6 carbon atoms, lower alkoxy of 1 to 6 carbon atoms, halogen, nitro or trifluoromethyl with the provisos that (1)when R¹ and R² or R² and R⁶ are both alkyl they are selected from normal and secondary alkyl groups and (2) when two alkyl R⁷ groups are present on the same carbon atom then they are both n-alkyl groups and when two R⁷ alkyl groups are present on adjacent carbon atoms they are selected from normal and secondary alkyl groups.
 2. A compound as claimed in claim 1, or an acid addition salt thereof with a pharmaceutically acceptable acid wherein R¹, R², R⁶, and R⁷ are the same or different and are selected from hydrogen and lower alkyl of 1 to 4 carbon atoms.
 3. A compound as claimed in Claim 1 wherein R¹, R² and R⁶ are selected from hydrogen and methyl.
 4. A compound as claimed in Claim 1, which has the formula ##STR11## or pharmaceutically acceptable acid addition salt thereof wherein R¹ and R⁷ are selected from hydrogen and alkyl of 1 - 6 carbon atoms.
 5. A compound as claimed in claim 1 which has the formula: ##STR12##
 6. The compound as claimed in claim 1 which is 8-cyano-5,6,7,8-tetrahydroquinoline.
 7. The compound as claimed in claim 1 which is a 8-cyano-2-phenyl-5,6,7,8-tetrahydroquinoline.
 8. A compound as claimed in claim 1, which is 8-cyano-3-methyl-5,6,7,8-tetrahydroquinoline or a pharmaceutically acceptable acid addition salt thereof. 